The correct option based on the context of the Fourteenth Amendment in relation to the Dred Scott decision is:
4. The Dred Scott decision declared that African Americans were not citizens, so the amendment defined citizenship to include them.
This option accurately reflects the historical context, where the Dred Scott decision denied citizenship to African Americans, and the Fourteenth Amendment was enacted to establish citizenship rights for all people born or naturalized in the United States, regardless of race.